western treatment plant
On this page:
The Western Treatment Plant is about 10,852 hectares. It treats about 52% of Melbourne's sewage, or about 485 million litres a day. This serves about 1.6 million people in the central, northern and western suburbs.
Sewage treatment at Western Treatment Plant
Birdlife
The Western Treatment Plant is a haven for thousands of birds and is recognised as one of the world's most significant wetlands.
In the past the plant used three sewage treatment methods: lagoon treatment, land filtration and grass filtration.
We stopped using land and grass filtration methods at the Western Treatment Plant in 2004. Today, the plant uses modern lagoon treatment methods.
Lagoon treatment
At the Western Treatment Plant, we have 3 modern lagoon systems.
A lagoon system is made up of 10 lagoons or ponds. Sewage flows slowly through these lagoons, allowing bacteria already in the water to break down the organic material. The water gets cleaner and cleaner as it flows through each of the lagoons.
There are two main types of lagoons used in lagoon treatment - aerobic (with oxygen) and anaerobic (without oxygen). This is because there are different types of bacteria that could survive in either environments. We need both types of bacteria to work together to break down the organic material and treat the sewage for us.
The first stage of lagoon treatment is anaerobic (without oxygen). An anaerobic lagoon has no oxygen because of the high amount of sewage in it. Sewage typically does not have oxygen.
Anaerobic lagoons can produce strong, unpleasant smells and release dangerous greenhouse gases. So, some of our lagoons are partly covered with methane covers. Covering these lagoons means that the unpleasant smells and the greenhouse gases can be captured. We use the captured gases, called biogas, as fuel to generate electricity to run the plant.
As sewage flows through one lagoon after another, more oxygen becomes available in the water. In some lagoons, a lagoon is aerated (air is pumped into the water using an aerator or diffuser) to introduce oxygen into the water. In other lagoons, it happens naturally. As lagoons becomes more aerobic (with oxygen), smells becomes less of a problem.
By the 10th lagoon, sewage is known as treated effluent, and is ready for the next stage of the water cycle.
Land filtration
Cattle and sheep
Some 15,000 cattle and 40,000 sheep graze on land at the Western Treatment Plant.
The land filtration method dates back to 1892, and was the main sewage treatment method for summer.
In this method, an open paddock was flooded with sewage, up to a depth of 10cm. The land acted as a filter - rubbish and other solids are filtered by the land, while the filtered sewage seeps through the soil, and flowed out at the lower end of the paddock into an earthen drain. The earthen drain then carried treated effluent to Port Phillip Bay.
Nutrients (for example ammonia from detergents) in sewage were used by the grass and pollutants were broken down by the bacteria in the soil.
The treatment process normally took about 3 weeks, and happened in cycles. It took about one to two days to flood the paddocks, and a further five days for the paddocks to dry out and for sewage to seep through the soil. Then, sheep and cattle grazed on the paddocks for about two weeks, before the land was flooded with sewage again.
Grass filtration
The grass filtration method was adopted in the 1930s as the main winter treatment method.
In the grass filtration process, sewage underwent 2 stages:
- Pre-treatment, and
- Filtration in grass paddocks
Large rubbish was first removed from the water in large concrete tanks through the process of sedimentation. Lighter rubbish floated to the top of the tank, while heavier rubbish sank to the bottom of the tank, leaving a middle layer of water called primary treated sewage.
The primary treated sewage then slowly flowed over sloping bays planted with a type of grass that was tolerant to continuous flooding. As sewage trickled through the grass, all other solids were filtered out. Pollutants in the water were removed by a film of bacteria which were present on the grass and in the soil. At the end of the bay, the filtered sewage flowed out into earthern drains which took the treated effluent to Port Phillip Bay.
Protecting the environment at WTP
In the late 1990s, we carried out the largest upgrade of the treatment process in the plant's history.
One of the main aims of this upgrade was to reduce the amount of nitrogen entering Port Phillip Bay. Our lagoons were enhanced with the latest technology to remove as much nitrogen as possible.
As a result, there is a reliable supply of high quality recycled water for farms, parks, market gardens and other uses.
Brief history
In 1892, the Melbourne and Metropolitan Board of Works began buying land west of the Werribee River to build Melbourne's first sewage treatment plant - the Western Treatment Plant.
The area around Werribee was chosen for the treatment plant for many reasons.
- The soils around the area were suitable for the land filtration, the first method the Melbourne and Metropolitan Board of Works planned to use to treat sewage.
- The area was dry enough for the treatment methods that were planned. Engineers would not have to worry about high rainfall patterns adding to the amount of water already on the treatment plant.
- It had mild weather (free from snow and ice) which was important for the natural methods needed to treat sewage.
A virtual tour of the Western Treatment Plant
The Western Treatment Plant Explorer is the ideal way to learn about Melbourne's sewerage system.